MacBook Air 2015, 820 00165 A, no backlight following liquid damage

[estelanim416]

Hi

Got this board yesterday
D7701
C7796
C7797
L7701 all looked awful so replaced them, but still no backlight, otherwise the unit is functional
Please assist

 

[2informaticos]

Do you get image on internal LCD?
Verify continuity between D7701 and A5 ball of U7701.
Post some voltages for U7701, Q7706, D7701.
Be sure F7700 is OK.

 

[estelanim416]

Yes, the picture is present when I put the light behind the screen

Q7706
1 - 8.12v
2 - 8.12v
3 - 2.67v
4 - 8.12v
5 - 8.11v
6 - 8.12v

D7701

both ends 8.08v

F7700
similarly, both ends 8.08v


I can't seem to find the test point for the 5th ball of U7701, my layout seems slightly different from the boardview I have :/

 

[2informaticos]

Scratch the board near the corner chip.
You'll find a small area going out from A5 pad...

Pay atention to XS7720, placed between L7701 and D7701.

 

[estelanim416]

XW7720 is not present on my board for some reason - looks like its some different variation

Tried scratching what seems to be a hidden pad but I am not sure if I did it right. No continuity. between ball 5 and D7701

 

[2informaticos]

It is there, but is damaged.
You can still solder a tiny wire from D7701 to the central point.
Or you can search Louis channel on YouTube and apply rescue method soldering a wire from A5 ball to a point from other side...

 

[estelanim416]

Thank you for all your help so far!
You mean XW7720 is there? Maybe I am thinking of something else, when I look at the boardview it is showing me this

But there is literally no room on my board for it as you can see on my previous photo.
I have a feeling I am using some bad brd file :/

When you refer to "Central point" I am not sure what do you have in mind?

 

[2informaticos]

https://drive.google.com/open?id=18UR9ufMnaWRTbwZwNjTTxmIcHGCNpSBl
Do you see it now???

 

[estelanim416]

It's a pad! I was expecting a component looking at the brd
Yes, there is a continuity between ball 5 and that pad

 

[JohnB8812]

Your issue is likely the feedback trace seeing that that pad is completely burned away. Run a wire from the LP8550 to the diode. Replace the driver and it should work

 

[Paul Daniels]

estelanim416 yes, in these macbook board files, "XW" prefix typically just means 'wire' / PCB track.

 

[estelanim416]

Cheers! I will get the driver and check it!

 

[2informaticos]

I just marked in red the trace you need to rebuild there...

 

[estelanim416]

Chhers, after I remove the driver I will pull the wire there then put a new driver, this should do it hm?

 

[JohnB8812]

Run the small wire 2informaticos suggested then check for continuity from the A5 ball to the diode. If you get continuity, then it will be fine. If not, you need to run the wire all the way to the other side of the board.

 

[estelanim416]

Thank you JohnB8812

ok, at the moment I have continuity from A5 to XW7720. The brd file suggests that XW7720 has two pads and the second pad should connect to pad 2 of the D7701

So I am guessing that your advice is to run a wire from XW7720 to pad 2 of D7701

 

[JohnB8812]

Yes run the wire then make sure it has continuity from the diode to A5. If so, replace the driver and you should be good.

 

[estelanim416]

FYI it worked like a charm

Thank you!

 

[JohnB8812]

Nicely done!